The present invention relates to the fabrication of a slider bearing at least one magnetoresistive sensor for data storage applications, and in particular to a magnetoresistive lap monitor which will control the lapping of the magnetoresistive sensors positioned on the surface of the slider such that the magnetoresistive sensors are lapped to a proper height.
Winchester style sliders having magnetoresistive (MR) sensors are used in magnetic storage systems to detect magnetically encoded information. A time dependent magnetic field from a magnetic storage medium or disc directly modulates the resistivity of the MR sensor. The change in resistance of the MR sensor can be detected by passing a sense current through the MR sensor and measuring the voltage across the MR sensor. The resulting signal can be used to recover information from the magnetic storage medium.
Practical MR sensors are typically formed using ferromagnetic metal alloys because of their abnormally high magnetic permeability. A ferromagnetic material is deposited in a thin film upon the surface of an electrically insulated substrate or wafer. Changing magnetic fields originating from the magnetic storage medium rotate the magnetization of the MR sensor and thereby change the resistance of the sensor. This phenomenon is called the MR effect.
An MR sensor has a maximum signal-to-noise ratio when the active region of the sensor has no magnetic domain boundaries. In other words, the active sense area of the MR sensor should be a single domain. The presence of domain boundaries in the active sense area gives rise to Barkhausen noise, a phenomenon caused by the irreversible motion of a magnetic domain in the presence of an applied magnetic field. Barkhausen noise cannot occur if no domain boundaries exist. Typically, a single magnetic domain MR sensor is achieved by either utilizing geometry or via boundary control stabilization, or both.
In order to efficiently form sliders for thin film recording heads, the following generic machining steps could be performed: (1) slice a substrate or wafer into a series of bars; (2) lap the bars to a final height while statistically monitoring all lap monitor resistors positioned across the bar for average height control; (3) define the slider rails; and (4) free the individual sliders from the bar.
Conventional lap monitors for inductive thin film heads are typically used to lap inductive head bars to a final height (step 2). Conventional inductive lap monitors typically utilize pole metalizations and polymers to form an analog-digital system for end point lap detection. These metalizations are common to the thin film inductive head write structures. However, with sliders having an MR head design positioned on the surface of the slider, the situation is much more complicated since the MR head is a combined MR read, inductive thin film write device. For proper MR reading, it is essential to control the end point lap detection of the slider surface bearing the pair of MR sensors by using features common to the MR sensors. The end point lap detection determines the final height of both the slider rail and the MR sensors. Since inductive thin film lap monitors utilize features common to inductive thin film writers, end point lap detection control of the slider and its MR sensors is degraded if writer based lap monitor resistors are used. This results from a variety of reasons, such as alignment tolerances.
Although one could also use the actual MR sensor as a lap guide, a number of factors have been found that result in a preference of the separate lap monitor resistor over that of using just the MR element. First, if the MR element is used as a lap monitor resistor, it is difficult to augment the device with additional structure for detecting faults and handling possible contact defects. Furthermore, stray ground loops in the lap machines or static discharge could damage the MR sensor.
Thus, standard factory inductive lap monitors are not suitable for MR heads having an MR reader and an inductive thin film writer. Therefore, there is a need for an MR lap monitor system which can accurately lap MR sensors on the surface of a slider to a proper final height using metalizations and other materials common to the MR element structure.